It is required in many textile and nontextile applications to be able to feed a strand from one point to the other at preselected varying rates of speed. One common use for such technique is in the application for the formation of air-textured core-and-effect yarns wherein a plurality of yarn strands are fed to an air texturing jet so as to entangle them into a composite yarn mass in particular manners dependent on the end product desired. In such technique, it is generally necessary to overfeed to varying extents one or more of the individual strands passing to the air texturing unit so as to emphasize either by color, texture or other physical property such yarn or yarns in the final assembly, i.e., a particular color yarn could be overfed at periodic intervals so that a greater proportion of such yarn color would predominate at such periodic intervals within the resultant yarn formed thereby. Similarly, multilevel slubs may be formed by application of similar techniques.
Mechanisms are heretofore known which periodically feed strand at such varying rates, such as, for example, the device disclosed in U.S. Pat. No. 3,805,344, which has particular utility in the specific air texturing processes above mentioned. This device includes first and second yarn feed rolls operating at different surface speeds. Each feed roll has an idler roll associated with it but spaced therefrom. Also included are means for alternatively moving one of the idler rollers against the feed roll with which it is associated so as to force yarn passing thereover against such feed roll to drive the yarn. This device, although being commercially used, does not maintain continuous control over the yarn as it is fed, inasmuch as each time the yarn is transferred from contact with one feed roll to contact with the other feed roll, the yarn is momentarily free to run out of the intended yarn path. The provision of control means to prevent such runout and to otherwise provide a more positive control requires the incorporation of highly critical alignment mechanism. Devices of this type are also not adapted for the simultaneous feed of a plurality of yarns at different rates.
It accordingly is desirable to provide strand feeding mechanism which enables one or more separate strands to be alternatively fed at varying rates of speeds, as for further processing to downstream work stations, such as the air texturing process above referred to, and to accomplish such while maintaining a high degree of control over each such strand.